Had a new people bring this up, when trying to login to a Synology NAS the message “Because the encryption key is invalid, the password has been transmitted as plain text without encryption.” is received.
The basically boiled down to trying to login via https on a non-https port, the default ports for the NAS are:
ip:5000 - http
ip:5001 - https
Attempting to connect to port 5000 using https will bring up this message, use port 5001!